Metal-insulator transition at low densities in a two-dimensional low-bandgap semiconductor

Metal–insulator transitions in low band-gap systems emerge from the interplay of interactions, disorder, and band structure on comparable energy scales. Platinum diselenide, with its thickness-dependent electronic structure, provides an ideal platform to explore this regime, as the five-layer limit lies close to the semimetallic boundary while retaining a small bandgap (~0.1 eV). Here we show that hexagonal boron nitride-encapsulated five-layer PtSe2 devices with embedded ultra-flat, pre-patterned platinum contacts exhibit high electronic quality, with mobilities up to 1,640 cm2V−1s−1 and contact resistances as low as 1.31 kΩ·μm at 1.5 K. These characteristics enable a gate-tunable metal-insulator transition at carrier densities down to 2.75 × 10¹⁰ cm⁻². Transport in this regime is dominated by electron–electron interactions, as supported by finite-temperature scaling. Below 50 K, however, an additional disorder-related energy scale emerges, consistent with percolation. These results demonstrate that disorder remains relevant even in high-mobility devices, challenging a purely interaction-driven transition in two-dimensional systems. The behavior of metal-insulator transitions can be impacted by interaction and disorder mechanisms. Here, the authors identify metal-insulator transitions at carrier densities on the order of 1010 cm−2 in PtSe2 devices and evidence of a crossover in the metal-insulator transition behavior.